The aqueduct is composed of colossal dressed blocks of masonry which were laid without mortar, the stones being held together with iron clamps. In order to break the monotony the three levels of arches are recessed, the piers in line with one another. The bridge was restored under Napoleon III. The architect varied the span of the arches very slightly within each range. The stones obtruding from the face were scaffolding supports, and were left not only to facilitate maintenance work but to add interest to the surface as do the ridges on the piers, which held the semi-circular wooden frames on which the arches were constructed.